Some good (painful) physics lessons in trying to put a 360 video rig under a drone

"9 Lessons Learned from Attaching a Super Heavy, Custom Rig to a Quadcopter": A very interesting post from Makezine and how to attach things to drones:

Recently, a company called 360.place contacted me about mounting a GoPro VR Rig to an Inspire 1 drone. Getting paid to work with new and interesting technology is pretty much the most fun an engineer can have, so I was thrilled to take on this challenge. After about a month of work designing and building the rig, I had something that the customer was pleased with, however, it definitely took some work to get things right. Here are a few of the lessons I learned on this project, as well as a few that I got right the first time!

When in Doubt, Measure or Weigh

At the start of this project, 360.place decided themselves what type of drone and camera they wanted to use. The good thing is that two of the project conditions were already taken care of, but on the other hand, I had my doubts about whether this drone could lift what we thought was a 5 pound weight. After the vehicle struggled to lift 4 pounds in a test video (not ours) seen below, a 5 pound weight plus whatever I needed to use to attach it seemed like it would be impossible.

Not having my arms “properly calibrated,” 5 pounds seemed like a good assumption after holding it, but when I went back to their office to discuss the project further, I brought a precision scale. Although I thought this might have been the end of the project, the rig actually weighted in at a much more manageable 2 pounds. It was time to start planning

Ideas Come… Eventually

An Early Design Idea

The obvious solution to mount this rig was to run some sort of rod down from the center of the DJI Inspire. This has been done before, but I didn’t see a good way to do it without modifying the quadcopter itself. For better or worse, when I can’t figure something out, it just tends to churn over and over in my head until I have a good solution. Perhaps I should figure out how to charge for these random “unguided brainstorming” sessions. On the other hand, listing “$300: staring off into space for several hours” on an invoice likely wouldn’t go over too well.

The final idea hit me while driving, “Why not mount it to the carbon fiber rods attached to the motors?” I’m not exactly sure how inspiration struck, but having 30 minutes or so where I was entirely free from distraction besides staring at the road really seemed to do the trick. Perhaps taking a break from everything once in a while is a good idea in the creative process. Just remember to note your great ideas down when they come!

Pay in Dollars or in Weight

One thing that struck me while doing this was how expensive carbon fiber and other lightweight components are. The rods attaching the camera rig carrier to the Inspire cost well over $100, and I purchased several components in aluminum that traditionally would be made out of steel. Add to that some machining time to take off extra material, and the costs really start to add up.

Angular Momentum Matters

The whole time I was designing this, I concentrated on weight and keeping the Inspire far away from the VR rig in order to keep the shots as clear as possible. Unfortunately, the farther away from the quadcopter the weight is mounted, the greater the angular momentum acting on it. As seen in the video below, before I reduced the length of the rods, things did not go well:

Or as Archimedes said: “Give me a lever long enough and a fulcrum on which to place it, and I shall move the world.” Perhaps today he’d also add, “…Or death-spiral a quadcopter.”

Test Incrementally

After the first failed experiment, we loaded up the quadcopter incrementally. First we just used the rig with no weight, then a lighter Samsung camera, and finally a weight representing the Omni. There was no real problem this time, but perhaps if we’d tried this procedure the first time, we could have avoided a crash.

Record Your Trials, Know When to Bail

The one upside to this crash was that we did record it from several angles. Besides perhaps being educational for others or even myself pursuing their own filming system, I found it quite entertaining.

One thing that may stick out is that while the pilot tried to go catch the Inspire, you can see me leaving. Though it might not look very “heroic,” having worked on and around machinery for many years, I always try to remember that your hands, eyes, or life isn’t worth whatever piece of equipment you’re working on. When things start to crash, in most cases it’s best just to let it happen.

Practice On Small Drones is Good

During this process, I said that I didn’t want to fly the drone, I’d leave it up to the customer. Probably a good policy, but while I had it to work on, I needed to do some landing gear testing and decided to take it up myself. I had permission, and had been assured that it was OK with the customer, but obviously didn’t want to crash their multi-thousand dollar quadcopter.

To my pleasant surprise though, the controls worked in the same manner as the little Hubsan drones that I’d crashed hundreds of times, and I was able to take off and land with no problem.

Don’t Take Risks with Other People’s Equipment

Though it was easy to fly with no payload, after trying it out myself, I requested to fly the entire rig during our final test. This wasn’t a problem initially, but when I decided to pull in for a landing I was a little off, tilting the quadcopter, and eventually causing it to topple and crash. Fortunately, there was no serious damage, but I was quite embarrassed. The gimbal mount was cracked (re-cracked actually, since I repaired it from the first crash), and one of my custom rod ends pulled out of the carbon fiber.

Not good.

Take All the Tools You Might Need

The good news on this though is that I brought everything I though I would possibly need to the test site. Once I’d examined the defects, within a few minutes I had epoxy drying in the appropriate places, and the drone’s normal pilot went on to film on location in a few days. Here’s some footage that he took:

Overall it was a successful project, and I hope I can help them with other projects in the future. If you’re interested in building your own rig, I put my design and bill of materials up here (with permission) as well as more information on the design process. I invite you to check it out, and hopefully this post helps you realize what went into building it!

Very interesting. And of the whole history I would remark the following phrase:

Perhaps I should figure out how to charge for these random “unguided brainstorming” sessions. On the other hand, listing “$300: staring off into space for several hours” on an invoice likely wouldn’t go over too well

Something I don't understand - you complain about lightweight components costing a lot of money ... then you go and use 4 legs = 4 times the material cost. And you don't exactly go slimline, it looks like you could stand on that thing without breaking it! Was there really not a 1 boom design option, with a couple of little linkages for the levelling?

Also, isn't a piece of string a perfectly good solution? it's a 360 degree camera at the end of the day therefore orientation doesn't matter - stabilise rotational movement in post-processing, job done. No?

I dont get it. They could have lifted 4 times that load for a fraction of the cost of some nearly useless product like the Inspire. Heck, even the hobbyking beerlift events pretty much show you how not to suck, and for low costs.

There are very many who have misunderstood how the drone keeps the balance.

Many believe that a drone keeping the balance in the same way as a sailing boat. A large keel with a weight makes it stable. It is a simple and attractive explanation. But wrong.

A drone keeps the balance in the same way as the ballerina at the circus dancing on the tightrope. Very many small quick corrections. Try adding a keel ... and the ballerina must now deal with the keel mass and movements ... small fast movements is not enough for this.

I built a mount for a 360 Gopro setup for my university about a year ago. Hard mounting is of course not an option, as it would impair the quadcopter's ability to stabilize itself. The uni had an Inspire 1 already, so they wanted to use that.

I used a two parallel 10mm CF tubes which were attached to the copter by a "hinge" made of slingshot tubing, which was then attached to ball dampers. This not only minimized the strain on the copter's ability to to roll and pitch, but it allowed them to land on the ground without having to use some elevated platform.

i used to mount 6 gopro under my hexacopter. Based on my experience... mount it only with one string attached to the body. So the camera attached to cg of your copter (make sure its free to move, not fixed joint). DO NOT Mount to each arm... it will swing your copter. I flipped one... crash to the ocean.......